Fashion is having a Mrs Simpson moment. No, it's not the first time we admit, but the streamlined chic that earned Wallis her style icon stripes completely chimes with the feel of fashion right now. We predict that Wallis 'Get the look!' features are set to spike very soon. Especially since W.E., Madonna's film about the American socialite's life, had its world premiere at the Venice film festival on Thursday. The film stars Andrea Riseborough and from the shots we've seen, the wardrobe looks brilliantly done, no matter what reviews make of scene where Wallis jives with an African tribesman to the Sex Pistols' Pretty Vacant.

That Dress: Roland Mouret's Wallis Simpson-inspired dress

Designer Roland Mouret is not shy about admitting his admiration for Wallis's style either. Next Tuesday he will launch a gold, embossed silk maxi-dress as a tribute to Mrs Simpson's wardrobe. "You can't work in fashion and not be inspired by the life and wardrobe of Wallis Simpson," he says. "Love or hate her, the world is still obsessed by that woman."

The concept of the dress - which was a highlight of Mouret's 2011 autumn catwalk - was, in his own words, "to bring together austerity and sensuality, shown by the boat cut of the neckline in contrast with the high split of the skirt. [It is] reminiscent of decadent 1930s nights and the fluid silhouette Wallis was known for."

The dress goes on sale on Net-a-Porter on Wednesday and will cost £2,100 (if you have access to that kind of cash; alas, we don't). Its launch will coincide with the publication of Anne Sebba's new book, That Woman: The Life of Wallis Simpson, Duchess of Windsor. The biography profiles Simpson's life and her relationship with Prince Edward and the royal family. In the article below, written exclusively for Guardian Fashion, Sebba examines Simpson's sartorial side. Imogen Fox

'She may not have been the most beautiful woman in the world, but she could make up for it by being the best dressed'

Wallis Simpson always used fashion as a weapon. Once she married the ex-King, henceforth the Duke of Windsor, what she wore took on an even greater significance. She may not have been the most beautiful woman in the world, but she could make up for it by being the best dressed. She believed she owed him this to make up for all he had given up.

From the day of her wedding onwards, 3 June 1937 - an event she hoped would be seen as an alternative to the coronation a few weeks beforehand – she was driven by rivalry with her sister-in-law, Elizabeth. She dubbed the new Queen "Cookie", and constantly poked fun at her frumpy, flowery outfits. This rivalry lasted until the Duke of Windsor's death in 1972. Wallis knew the world's eyes would be upon her at his funeral, and she was grateful to Hubert Givenchy for staying up all night to make sure her plain black coat and waist-length chiffon veil was the epitome of understated chic. At 76 she looked as elegant as ever, and could not resist remarking to friends later how amusing she found the Queen Mother's outfit, especially the hat which she described as looking as if a white plastic arrow had been shot through it.

A portrait of Wallis Simpson from the 1930s. Photograph: Off/AFP/Getty Images

One of the most telling images in The King's Speech is the Duchess of York, later the Queen Mother, with her two sweet-faced daughters in blue-sashed party dresses, strappy sandals and white ankle socks, representing the perfect family. Wallis, in her backless cocktail gown, appears as the antithesis to this home-loving, mumsy image - not only because she was divorced but because of her quick wit, sharp tongue and equally sharp clothes.

Her potent mixture of glamour and sexual allure seemed to pose a terrifying threat to many women in 1930s Britain, where divorce was fiendishly difficult, expensive and not available to women if they too had committed adultery. It was better to remain stoically unhappy if the alternative was your husband simply waltzing off with another woman and abandoning the family. Not surprisingly, the 500,000 strong Mothers' Union opposed any relaxation of the divorce laws and women like Wallis, who led free and easy lives with money to spend on clothes not curtains, were, quite simply, too dangerous.

Ever since her days as an impoverished Baltimore debutante who took a bus to visit Ellen, the seamstress, young Wallis Warfield had clearly defined ideas about clothes and celebrities whose outfits she wished to copy. Marrying Ernest Simpson - plus a small legacy - gave her a little money to go to Paris and buy some haute couture dresses she could ill-afford, in readiness for a meeting she hoped would soon come with the Prince. When it did, she was well prepared.

In the early days of her royal romance she made some fashion faux pas. On the famous Nahlin cruise in 1936 Lady Diana Cooper, a fellow guest, poked fun at a childish white cotton piqué bonnet. Later, her craving to be first with the latest fashion led to sequinned hot pants on one occasion and a Paco Rabanne space suit on another, while her muscular shoulders were less than ideal when it came to strapless evening gowns. But mistakes were rare and from now on her dress style was sophisticated and classic, if sometimes severe.

With money came access to the best couture houses in Paris and she attended many fashion shows in the front row, cultivating her favourites: Givenchy, Schiaparelli, Dior and Mainbocher - the latter responsible for her wedding dress. Wallis knew this would be one of the most important outfits she would ever choose, as it needed to convey not just to the British in 1936 but to posterity what they missed by rejecting her. It is surely no accident that her hat was in the shape of a halo and at her wrist she displayed a bracelet of crosses, gifts from Edward to mark milestones in their relationship. She was using fashion to convey a message.

The Duke and Duchess of Windsor pictured in 1954. Photograph: PA

The Duke believed Wallis, having given up so much in terms of reputation in order to marry him, must be rewarded if not with a royal title then with jewels fit for a royal consort. This dictated the style of many of her clothes, which had to be beautifully cut to show off her impossibly thin, bony frame, and never fancy or flowery in order to show off the magnificent jewellery. One diarist of the day described her as "literally dripping" with rubies. Keeping herself stick-thin was vital and she gave precise instructions to her cook about the weight of a steak; if she was a pound overweight one day she would have only a boiled egg for lunch.

Modern women may find it easier to understand Wallis's sharp, elegant dress sense. And there is a sound historical reason for revisionism: painting Wallis in the worst possible light was deemed necessary in those critical years of the later 1930s, in order to boost the insecure and stammering Bertie and his strong wife in her flowery hats.Anne Sebba

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